Classes Implementing Interfaces
A Slice class can also be used as a servant in a server, that is, an instance of a class can be used to provide the behavior for an interface, for example:
interface Time {
idempotent TimeOfDay getTime();
idempotent void setTime(TimeOfDay time);
};
class Clock implements Time {
TimeOfDay time;
};
The implements keyword indicates that the class Clock provides an implementation of the Time interface. The class can provide data members and operations of its own; in the preceding example, the Clock class stores the current time that is accessed via the Time interface. A class can implement several interfaces, for example:
interface Time {
idempotent TimeOfDay getTime();
idempotent void setTime(TimeOfDay time);
};
interface Radio {
idempotent void setFrequency(long hertz);
idempotent void setVolume(long dB);
};
class RadioClock implements Time, Radio {
TimeOfDay time;
long hertz;
};
The class RadioClock implements both Time and Radio interfaces.
A class, in addition to implementing an interface, can also extend another class:
interface Time {
idempotent TimeOfDay getTime();
idempotent void setTime(TimeOfDay time);
};
class Clock implements Time {
TimeOfDay time;
};
interface AlarmClock extends Time {
idempotent TimeOfDay getAlarmTime();
idempotent void setAlarmTime(TimeOfDay alarmTime);
};
interface Radio {
idempotent void setFrequency(long hertz);
idempotent void setVolume(long dB);
};
class RadioAlarmClock extends Clock
implements AlarmClock, Radio {
TimeOfDay alarmTime;
long hertz;
};
These definitions result in the following inheritance graph:
A Class using implementation and interface inheritance.
For this definition, Radio and AlarmClock are abstract interfaces, and Clock and RadioAlarmClock are concrete classes. As for Java, a class can implement multiple interfaces, but can extend at most one class.